1. Field of the Invention
This invention relates to a method of manufacture and the manufactured article. More specifically, this invention concerns itself with an improved technique for the fabrication of flexible shafts for endoscopic instruments and the products which result from this improved technique.
2. Description of the Prior Art
The advent of flexible endoscopes has made possible the invasive, non-surgical examination of the gastrointestinal tract. As is readily appreciated, the more compliant and flexible the shaft of these instruments, the less discomfort experienced by the patient during examination by the physician. The flexible shaft of such instruments is typically formed by spiral winding a ribbon of metal in the form of a helix. The helix can thereafter be soldered on either end to a tubular element which forms the point of attachment to the control head of the instrument and to the objective assembly. In order to increase torsional stability of the helix, the ribbon spiral is further enveloped in a mesh-like material which in turn is further enclosed by a flexible plastic sheath. Typically, the interior of shaft will also include various guides or other means for segregating the control wires, optical bundles and instrument channels which course through it from the control head to the distal end of the instrument. U.S. Pat. No. 2,243,922 (to Wappler) is illustrative of the type of instrument described hereinabove.
Various fabrication techniques are known to effect the resiliency of the flexible shaft suitable for use in endoscopic instruments. These techniques include varying the thickness and/or width of the ribbon used in the fabrication of the spiral tube; selection of metals of varying hardness for such ribbon and the construction of the flexible tube by physically or mechanically joining together two spirals of dissimilar flexibility. Where this latter practice is followed, there is generally an abrupt transition in flexibility from one segment of the flexible shaft to another. Not only is this undesirable, but dramatically increases the cost of fabrication of the flexible element and the potential for failure at the junction where such similar elements are joined together.
Another technique commonly employed in the construction of flexible shafts for endoscopes is described in U.S. Pat. No. 3,799,151 (to Fukaumi et.at). In FIG. 2 of the '151 patent, a deflectable tube for an endoscope is constructed by the joining together of individually hinged segments wherein the hinged axis between each successive segment is perpendicular to the other when the tube in in the normally extended position. U.S. Pat. No. 4,108,211 (to Tanaka) also shows a deflectable tube structure formed of segmented vertebrae whose deflections are controlled by wires. Another expedient for imparting flexibility to a tubular member involves the executing of a predetermined number of cuts or slots in the tube wall, see e.g. FIG. 7 of U.S. Pat. No. 4,134,405 (to Smit).
All the expedients described heretofor in the fabrication of flexible shafts for endoscopic instruments, and the like, suffer from one more of the following shortcomings which include: (a) complexity of manufacture, (b) inability to readily form a shaft of unitary structure having either uniform or variable flexibility, and/or (c) inability to readily form a shaft of unitary structure having progressively variable flexibility without an abrupt transition between such areas of dissimilar flexibility.